This invention relates to modified liquid crystalline polymer (LCP) composites, and in particular to liquid crystalline polymer composites useful in the formation of circuit materials, circuits, and multi-layer circuits.
As used herein, a circuit material is an article used in the manufacture of circuits and multi-layer circuits, and includes circuit laminates, bond plies, resin coated conductive layers, and cover films. These circuit materials are each formed from a dielectric composition that can be a thermosetting or thermoplastic polymer. The polymers are often combined with fillers such as silica to adjust the dielectric or other properties of the composition. The dielectric material in a bond ply, resin covered conductive layer, or cover film may be substantially non-flowable, i.e., it softens or flows during manufacture but not use of the circuit, whereas the dielectric material in a circuit laminate (i.e., a dielectric substrate) is designed to not soften or flow during manufacture or use of the circuit or multi-layer circuit. Dielectric substrate materials are further typically divided into two classes, flexible and rigid. Flexible dielectric substrate materials generally tend to be thinner and more bendable than the so-called rigid dielectric materials, which typically comprise a fibrous web and/or other forms of reinforcement, such as short or long fibers or fillers.
A circuit laminate is a type of circuit material that has a conductive layer fixedly attached to a dielectric substrate layer. Double-clad laminates have two conductive layers, one on each side of the dielectric substrate. Patterning a conductive layer of a laminate, for example by etching, provides a circuit. Multi-layer circuits comprise a plurality of conductive layers, at least one of which contains a conductive wiring pattern. Typically, multi-layer circuits are formed by laminating one or more circuits together using bond plies, and, in some cases, resin coated conductive layers, in proper alignment using heat and/or pressure. The bond plies are used to provide adhesion between circuits and/or between a circuit and a conductive layer, or between two conductive layers. In place of a conductive layer bonded to a circuit with a bond ply, the multi-layer circuit may include a resin coated conductive layer bonded directly to the outer layer of a circuit. In such multi-layer structures, after lamination, known hole forming and plating technologies may be used to produce useful electrical pathways between conductive layers.
A variety of polymeric dielectric materials are used in circuit materials, circuits, and multi-layer circuits, including liquid crystalline polymers. There is a growing demand, however, for circuit materials for high performance (high frequency) applications, that is, applications operating at 1 gigahertz (GHz) or higher. High performance applications require, among other things, circuit materials having low dielectric constants for low propagation delay, lower cross talk and higher clock rates, low dissipation factor (Df) for low attenuation, better signal integrity, and lower power consumption in portables. Despite their utility as dielectric materials for circuit boards, liquid crystalline polymers further display a continuous modulus reduction above their glass transition temperature, which results in poor mechanical integrity at high temperatures. This can also result in lowering of copper bond strength, due to the poor cohesive strength of the films at high temperatures. This is not desirable as it causes lifting-off of copper pads during rework operation. There accordingly remains a continuing need in the art for dielectric materials that that meet the ever more stringent standards required for such materials, including acceptable electrical properties such as dielectric constant (Dk) and low dissipation factor, as well as excellent thermomechanical properties.